Searches for lepton flavour violation in the tau -> 3mu decay with the ATLAS Experiment

味道不是一种基本的对称，我们知道在标准模型（SM）中，中微子和夸克的混合都违反了它。因此，期望带电轻子味道破坏（cLFV）是很自然的，但是，尽管在g-2实验和B工厂中暗示了味道异常，但它从未在自然界中被看到过，它的观察将是超越SM物理的明确证据。虽然在电子和介子通道中已经设置了严格的限制，但在tau情况下的限制要弱得多。由于新的物理学很可能与较重的tau结合得更强，因此这是一个理想的搜索地点。该项目将使用gold tau - bbb30 μ子通道，在其干净的最终状态下，使用完整的run-2和部分run-3 ATLAS数据来搜索LFV tau衰变。学生将首先分析重味衰变中产生的tau，开发估计背景的方法和提取信号的多变量技术。在此之后，这项工作将扩展到W玻色子衰变产生的结果和两种搜索结果的结合。总之，这些有可能提供超过当前极限的灵敏度，并且，如果没有观察到新的物理现象，将对LFV tau衰变设定最严格的限制。该小组之前在W玻色子测量和最终态的搜索方面都有丰富的经验。

Flavour is not a fundamental symmetry and we know that it is violated in theStandard Model (SM), both in the neutrino- and quark-sectors, via mixing. Itis thus natural to expect charged lepton flavour violation (cLFV) but, despitehints of flavour anomalies at g-2 experiment and B factories, it has neverbeen seen in nature and its observation would be unambiguous evidence ofbeyond the SM physics. While stringent limits have been set in the electronand muon channels, the constraints in the tau case are much weaker. Sincenew physics is likely to couple more strongly to the heavier tau, this makes itan ideal place to search. The project will search for LFV tau decays using thefull run-2 and partial run-3 ATLAS data using the golden tau -> 3 muonchannel, with its clean final state. The student will first analyse tau producedin heavy flavour decays, developing methods to estimate the backgroundsand multi-variate techniques to extract the signal. Following this, the workwill be extended to taus produced in W boson decays and the results of thetwo searches combined. Together, these have the potential to providesensitivity beyond the current limit and, if new physics is not observed, setthe most stringent limit on LFV tau decays. The group has previous wideexperience in both W boson measurements and searches in tau final states.